diff --git a/srcpkgs/mozjs91/update b/srcpkgs/mozjs91/update
new file mode 100644
index 00000000000..f942fe4f0fc
--- /dev/null
+++ b/srcpkgs/mozjs91/update
@@ -0,0 +1,2 @@
+site="${MOZILLA_SITE}/firefox/releases/"
+pattern="releases/\K${version%%.*}.*(?=esr/\")"